Frequencies for phaz_cno variable in parkwork dataset :

  hazardous |
  materials |
involvement |
/placard-hm |
    4 class |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      1,088       99.91       99.91
          3 |          1        0.09      100.00
------------+-----------------------------------
      Total |      1,089      100.00

by Jean Roth , jroth@nber.org , 22 Oct 2016